Local load effects on road bridges
M. PRAT and B. JACOB
On bridges, the increases for dynamic effects
are
related to
4
factors
that
may,
in
consequence, induce unauthorized loads:
LOCAL LOAD EFFECTS ON ROAD BRIDGES
M. PRAT and B. JACOB
1
-
INTRODUCTION
The purpose of this paper is to present an
overview of a large number of experimental
results concerning the local traffic loads,
static
and
dynamic,
transmitted
to
road
bridges via the tyres of heavy goods vehicles
in normal operating circumstances.
A few
extreme cases, due to accidental situations,
are also considered.
These thoughts and analysis results concern
the origin, kinematics, and distribution of
loads on the decks of bridges, and have been
produced with a
regulatory aim,
for
the
generation of EUROCODE I
(Part 3) on road
traffic loads ([1), (2); the objective is to
define load models applicable to the design
of structures.
2
LOCAL
VEHICLES
LOADS
INDUCED
BY
HEAVY
GOODS
The action of a heavy vehicle on a bridge
includes a quasi-static component, determined
by its mass and invariant during a trip, and
a variable dynamic component, caused mainly
by the vibrations of the vehicle induced by
the irregularities of the pavement.
These
oscillations of the sprung masses (cab, body,
etc.)
and of the unsprung masses
(axles,
wheels, etc.) increase the loads transmitted
to as much as twice the static load.
2.1
-
Static
load
The static loads of the vehicles, measured
when stopped,
are subject to regulations.
Below the legal limits, they present no risk
to structures of which the design is calculated using correctly measured characteristic values with allowance for factors of
safety. These static loads result in pressures
on the soil that are distributed over small
areas - the contact surfaces of the tyres.
2 .2
-
Dynamic
the quality of pavement evenness;
the condition of the suspensions of the
vehicles;
- tyre/road interaction;
the dynamic responses of the bridges to
excitation by traffic.
Wearing course surface defects, combined with
the speed of the vehicle, initiate vibratory
phenomena that go through a number of "two
-way" filters
(suspension, shock absorbers,
etc ... ) and set in motion, selectively, from
bottom to top, at specific frequencies, all
of the sprung masses, whereas the un sprung
masses act more directly and rather rigidly
on the pavement (elastic impacts).
For a loaded truck wheel the
sprung masses to the unsprung
the vicinity of 7.
ratio of the
masses is in
Table 1 gives a few ranges containing the
usual frequencies and the amplitude of the
corresponding impact factors.
It should be
noted that the dynamic loads are not proportional to the static loads and depend on
many parameters. Thus, observations show that
the highest IFs are measured on vehicles with
lightly loaded axles (3). However, in this
case the equivalent total loads remain below
the values obtained for the most heavily
loaded vehicles, which have weaker vibrations.
TABLE 1
Frequency
of
resonance
(Hz)
Impact
IF
Sprung
masses
Unsprung
masses
[1 to 6)
[6 to 20)
[1.1 to
1. 4)
[1.1 to
1. 7)
I
Axle
peak
[12 to 15)
I
load
The dynamic loads (in what follows, this term
will be used only to refer to the dynamic
portion of traffic loads) are superimposed
on
the
static
loads
and may cause
the
authorized loads to be exceeded. They are
stated either in the form of additive forces,
dynamic loads added to the static loads, or
in the form of a
total equivalent
load
obtained from the static loads by multiplication by a impact factor ("IF").
156
-
3
-
TYRE/ROAD/BRIDGE
INTERACTION
Differences of relative level in the pavement
profile are in most cases the origin of
dynamic loads. But the braking forces of the
vehicle also induce vibrations and dynamic
loads. Finally, an instantaneous deformation
of the deck of a
bridge also engenders
vertical movements of the vehicle.
Heavy vehicles and roads: technology, safety and policy. Thomas Telford, London, 1992.
VEHICLE - BRIDGE INTERACTION
3.1 - Quality of pavement evenness
When an axle moves, it engenders degradations
of pavement evenness, which will in turn
initiate and amplify further excitations of
vehicles; these will add more damage that
will contribute to damage of the structures
and to the user's discomfort and unsafety.
It is therefore essential to attentively
monitor the evolution of the longitudinal
profile of a pavement and to be able to
measure it in order to decide on the justification of a maintenance action.
Analyseur de Profil en Long (APL)
3.1.1
[ 4]
In France, the LCPC has developed a system
called APL intended for investigation of the
evenness of pavements and the rapid qualification of highway routes. variations of
level of the road surface are translated into
a function combining elementary analog signals
that may be continuous (waves) or discrete
(joints). Computer processing of the profile
function breaks the signals down into wavelength bands L.
On the basis of these
"full-scale"
wavelengths
and
an
energy-per-band criterion, an evaluation scale
makes it possible to characterize the effect
of variations of level for various applications, mainly those that are relevant to the
local loads of axles and vehicles on bridges.
We distinguish 3 types of application: the
"macrotexture" type (2mm<L< 2cm), the "short
distance evenness" type (2cm<L< 50cm), and
the "long distance evenness" type (50cm<L<
50m) .
TABLE 2 - Mean maximum difference of
level (mm)
Macrotexture
type
Short
distance
evenness
type
Long
distance
evenness
type
Good
evenness
1
2
10
Medium
evenness
2
6
20
Poor
evenness
5
15
50
Quality of
pavement
evenness
3.1.2 - Application of measurements
various inspections and ratings of pavements
are based on the APL measurements. All of
the results, used for many simulations, are
centralized and stored in the SETRA's Road
Data Base. In addition to some special studies
relating quality of evenness, comfort, and/or
safety, the APL is used both in the completion
inspections of new structures and in management follow-up of existing assets. It is
also used to measure the discontinuities of
the profile and to determine, for a given
section, an Evenness Discontinuity Index [4]
that is very useful in characterizing concrete
pavements and the wearing courses of bridges.
3.2
Effect of a discontinuity of road
profile
The passage of a tyre over an obstacle induces
a vertical force that may be treated as an
elastic impact. The force is greatest on the
edge of the obstacle. The response time of
the axle is greater than the duration of the
shock (frequency 10Hz) and it is the tyre
that,
by
being
crushed,
and
therefore
undergoing an increase of contact area, and
a temperature rise, transmits, over the length
of the obstacle, all of the dynamic load.
In the case of bridges, the dynamic load
caused by the impact depends on the length
of the span.
The peak increases occur when
this length is close to 5 metres and the
impact factor can then reach 2.3 for obstacle
heights of 3 cm and speeds less than 100
km/h. This factor falls to the vicinity of
1.7 for a span of 10 metres. Beyond 20 metres,
the bridge absorbs part of the impact and
acts in a sense as a shock absorber. We do
not find this phenomenon with pavements.
The table below gives experimental impact
factor values on pavements versus the shape
of a few obstacles.
TABLE 3 - Effect of vehicle rebound
[J
cle
Height Time of
h
passage
(cm)
(s)
Stiffness
of
tyre
Place of
maximum
action
IF
Manhole
cover
1
<0.01
0.6
On
obstacle
1.6
Bump
1
<0.01
-
20 cm
behind
the
obstacle
1.4
Hollow
2
<0.01
Reduces Behind
the
the
load
obstacle
1.5
When the differences of level are longer
(potholes or humpbacks), the time of passage
becomes greater than the excitation time, the
sprung and unsprung masses start vibrating
gradually,
and this movement substantially
attenuates the effect of the impact.
For the reasons reported above, smaller values
may be used for bridges.
3.3 - Braking
The longitudinal and transverse forces that
can be mobilized on bridges by trucks are
generally related to braking and to centrifugal forces and depend on coefficients of
friction
that
involve
the
qualities
of
adherence of both the tyre and the road [5].
The table below gives
a
few values of
coefficients.
157
HEAVY VEHICLES AND ROADS
TABLE 4 - Coefficient of friction
Vehicle
Longitudinal Transverse
Truck
Private
car
Formula
1
Rainy
weather
0.5
0.4
0.4
1
0.4
0.4
2.5
The braking distance is proportional to the
square of the speed divided by the coefficient
of friction. It is therefore beneficial to
have a high coefficient of friction. But if
this
coefficient
becomes
too
large,
the
accelerations that can be mobilized during
braking may cause skids or wheel hop that
are harmful in several ways: safety, load
transfer onto a limited number of axles, etc.
Improvements of surface characteristics must
therefore be accompanied by improvement of
the roadholding of vehicles during braking:
anti-locking devices for example. In any case,
the shorter the stopping distance the greater
the dynamic load on the bridge.
3.4 - Distribution of load
The loads applied to the decks of bridges
are distributed, at the level of the pavement,
over contact surfaces of which the contour
(shape) depends on the type of tyre used.
But in reality the load is diffused into the
mass of the bridge and acts structurally at
the level of the midplane. The active zone
of load distribution is thus larger than the
contact surface.
Studies performed in particular in the United
States [6] have shown that the pressures due
to high loads decrease with depth inside the
slab, spreading with a 1/1 ratio of linear
plan dimensions to depth.
But it is important to report that the
pressure under the tyre is not always uniformly distributed. In accidental situations
like sudden braking, a skid, wheel hop, or
the onset of aquaplaning, pressure concentrations appear under some favoured zones of
the tyre, and these transmit the load to
midplane of the structure in a harder manner.
A static load of 220 kN induces, for short
spans, a sag of between 0.3 and 30 mm,
depending on the bridge. The mean is in the
vicinity of 1.3 mm. Neglecting the dynamic
aspect, a bridge with a maximum difference
of level can therefore be compared, from the
point of view of the effect, to a pavement
of the poor long distance evenness type. The
bridge in efect amplifies
long-wavelength
evenness defects.
An important characteristic of the dynamic
behaviour of a bridge is its frequency [8].
Many standards in fact prefer to relate the
dynamic load to the frequency of the bridge
rather than to other parameters such as the
mean of the spans or the ratio of live loads
to permanent loads ([9], [10]). Generally the
frequencies of bridges are greater than 1 Hz
and rarely exceed 15 Hz, with a mean of 4
Hz.
Two types of coupling can therefore exist:
axle/bridge for frequencies greater than 6
Hz and, in most cases, sprung masses/bridge
for low frequencies.
4 - CHARACTERISTICS OF TYRES
The tyre transmits the propulsive force and
the load of vehicles to the structure. It
acts both as a spring and as a shock absorber.
It transmits and filters the action on the
pavement according to its own characteristics,
coupled to those of the vehicle, the pavement,
and the bridge.
To better understand the loads on bridges,
it is therefore important to have a thorough
knowledge, via the mechanical and geometrical
characteristics of the tyres, of the extreme
dynamic behaviours of vehicles. But these
extreme
behaviours,
which
depend on
the
technical capacities of the tyres, can be
known.
In effect,
standards require manufacturers to mark, on the sidewalls of tyres,
a number of coded letters and figures having
to do with (see figure 1):
The loads may then be distributed over a
third of the contact surface and be diffused
into the concrete along an oblique close to
the vertical.
3.5 -
Dynamic
response
of bridges
Bridges have the particularity of deforming
elastically and vibrating under the dynamic
action of heavy vehicles. Calculations [7]
have shown that the flexibility of bridges,
whether old masonry bridges or lightweight
metallic structures, does not exceed certain
limits.
Figure 1
158
VEHICLE - BRIDGE INTERACTION
- the maximum width S of the tyre,
- the maximum height H of the tyre (H/S close
to 0.8),
- the structure of the tyre (radial, diagonal,
mixed carcase (this last rare»,
- the inside diameter <I> of the rim,
- the type (single, wide, paired tyres),
- the maximum load capacity,
- the maximum speed V or speed symbol from
which the pressure can be deduced.
4.2
-
Contact
surface
Two
main
tyre
architectures
are
used:
diagonal carcases are used for aircraft and
farm tractors and radial carcases for almost
all road vehicles. We shall speak here only
of radial tyres, the particularity of which
is that they can be deformed by crushing only
longitudinally.
More detailed analysis of this information
is therefore very useful for the definition
and prediction of local loads on bridges.
4.1
-
Authorized load
A few maximum loads per axle
in conformity with European
given in tables 5 and SA.
and per wheel
standards are
TABLE 5 - Tyres with radial carcase for
trucks
Max.
load
/axle,
single
wheel
(kN)
Max.
load
/axle,
twin
wheels
(kN)
Tyre
pressure
(bars)
max
in
kph
20
85
150
9.25
70
Urban
area
20
110
198
6.75
65
Special
<I>
Rim
dia.
(inch)
24
80
146
7.5
V
105
Use
Road
TABLE SA - Tyres with radial carcase for
industrial vehicles
<I>
Rim
dia.
(inch)
Max.
load
/wheel,
driving
axle
(kN)
Max.
load
/wheel,
trailer
(kN)
Tyre
pressure
(bars)
max
in
kph
15
55
50
10
10
Trailer
road
24
177
10
5
Road
25
369
7
5
Road
/track
V
Use
Diagonal tyre
Radial tyre
Figure 2
The load is applied to the wearing surface
only on a limited area, always changing, and
the mean pressure "p" on the ground is equal
to
the
inflation pressure
"Pg"
plus
the
structural reaction of the tyre, which remains
small. The footprint of the heavy load is
substantially
a
rectangle
of
which
the
transverse dimension "b" is constant.
If we assume P=Pg,
we can deduce,
as a
function of the possible crushing "f=R-R f " of
the
tyres,
the
longitudinal
dimensions
a=2 [f (2R-f) ]'/2 of the corresponding contact
surfaces (R is the radius of the tyre with
no load and Rf the radius of the tyre under
the maximum load).
The maximum loads per wheel or per axle may
be reached or even exceeded.
The
speeds
permitted by the tyres are sometimes high,
often far higher than the legal speed limit.
One should therefore expect to find large
static loads on roads because of the behaviour
of road carriers. The rolling conditions may
also induce dynamic loads leading to the
technical limits of use of the tyres, which
gradually deteriorate and so also damage the
pavement. The study of tyre wear accordingly
provides
information
about
the
extreme
conditions of use and shows that there exists
a high probability of occurence even of loads
regarded as exceptional.
159
HEAVY VEHICLES AND ROADS
4.3
Table 6 - Tyres with radial carcase
for industrial vehicles
<11 of
rim
(inch)
D=2R
tyre
with
no
load
(mm)
Radius
R'
of
tyre
under
load
(mm)
S
H/S
b
mm
mm
mm
a
max
mm
Use
19.5
1098
494
477 .65 470 480
20
1348
611
412
412 570
Road
/track
24
1257
570
338 .65 338 527
Road
/track
15
934
420
278
278 420 Trailer
25
1744
795
671
671 716
Road
Selfpropelled
crane
We find that the impact surfaces on roads
are rather square and that in any case, under
load, the transverse dimensions are less than
or equal to the longitudinal dimensions.
Concerning the dimensions of impact, another
point deserves to be reported. Road carriers
have, for some time, stated their preference
for the wide single wheels of semi-trailers
over the old twin wheels, which are still
used for construction site trucks and some
driving axles. The advantages of the wide
single wheel are undeniable from the standpoint of:
safety (lowering of centre of gravity of
vehicles,
effect
of
improved
suspension,
better
load
distribution,
gains
in
load
volume,
elimination
of
risks
of
blowout
because of the frequent pressure differential
between the twin wheels),
- savings of sets of tyres (reduction of the
unsprung masses),
- consumption (lower rolling resistance, tyres
with more flexible sidewalls),
damage
to
pavements,
less
aggressive
skidding, etc.
The contact area of wide tyres on the extrados
of the skeleton of a bridge is calculated
from a transverse dimension equal on average
to 400 mm and a longitudinal dimension that
is
a
little
larger than
the transverse
dimension in a dynamic situation.
To correctly represent the coupling between
the phenomena, the formula below gives the
axle load Q in function of the pressure p
for a given speed and a contact area a little
larger than 400x400mm2.
Q=22(p+0.7) < 140kN
This type of wide tyre is already fitted on
most heavy industrial vehicles and will tend
to be used generally. The bridge· designer
cannot ignore this reality and must take the
corresponding type of contact surface into
account
in
his
calculations,
punching
included.
160
-
Pressure
in tyre
The pressure in the tyre, a function of the
load and of the speed, is the decisive factor
in the potential dynamic load. This pressure
is not constant because, when the vehicle
rolls, the temperature rise caused by the
various friction causes a normal increase of
the pressure, then stabilizes if the tyre is
initially correctly inflated. If the tyre is
underinflated, the temperature rise is greater
and the damage
to the
tyre may become
irreversible (formation of an unstable mixture) because then the equilibrium pressure
"no longer supports the tyre".
The rigidity of the tyre is related to the
pressure. In the stopped condition, the tyre
behaves like a linear structure: deflection
proportional
to
load.
But
this
rigidity
evolves with the speed in the course of
rolling. In terms of deflection, curiously,
experience shows that the rigidity decreases
with increasing speed, whereas the pressure
increases. But this is primarily a problem
of the modelling of the tyre. The boundary
conditions of the body representing the tyre
must also be incorporated in a global model
of the energy at large deformations type. The
phenomena involved are very complex and can
not be reduced to a simple linear elastic
model.
4.4
-
Internal tyre
impact
factor
We have just seen that the pressure in a
tyre depends on the speed. The characteristics
of tyres are stated by the manufacturers in
relation with the conditions of use, the
dimensions, and the type of tyre. For example,
a truck tyre that can roll at 100 kph can
be loaded in the stopped condition with 2.5
times the reference load at 100 kph.
The same technical data sheets also show that
the pressure capacity can vary under identical
conditions in a ratio of 1 to 1.4 as the
speed decreases from 120 kph to zero. Physically, the pressure must therefore remain
less than 1.4 times the nominal pressure.
This coefficient acts on the rigidity of the
tyre, itself a factor in the dynamic load.
We obtain here, in another way, a new estimate
of the impact factors. The global dynamic
coefficient,
related most directly to the
total load, must be compared to the factor
of 2.5 likely to affect the loads as a whole.
On the other hand, the local coefficient,
related most directly to the rigidity of the
tyre, can be compared to the factor 1.4.
4.5
-
Summing up
Considered from the standpoint of the tyre
alone, the foregoing considerations confirm
the type and extent of the dynamic loads.
But the action of a vehicle is not limited
to the action of a single axle. Whence the
idea of measuring the aggressiveness of a
train
of
axles
by
comparison
with
the
aggressiveness of a reference axle.
VEHICLE - BRIDGE INTERACTION
Not counting the direct action on the pavement
of the bridge, to a first approximation, we
note that, under regulation loading conditions,
the aggressiveness of tandems and
tridems is at least comparable to that of
heavy axles acting alone. Similarly, a 10 %
overload of an axle leads to twice the
aggressiveness
of
the
axle
loaded
in
conformity with regulations.
Knowledge of tyres and of the use made of
them in consequence gives a good approximation
of the loads that can be mobilized on bridges.
But this knowledge adds, to the complexity
of the loads, the complexity specific to the
tyres. Many more studies will be needed to
correctly delimit the domains.
5
-
DISTRIBUTION OF MEASURED
LOADS
The determination of the local loads to be
taken into account in the design of structures
must, in addition to the conceptual aspects
developed above, be based on the available
actual data. This is in particular a matter
of gathering and processing data on the
important descriptive parameters. It happens
that since 1980, weigh-in-motion systems have
been considerably developed, in particular in
France with the use of piezoelectric sensors
and the associated weighing stations [11].
This has made it possible to collect an
enormous mass of information on the weights
and dimensions of heavy vehicles and their
axles. This has also been done in other
countries of the European Community. On the
occasion of
the
work
of
preparation
of
Eurocode 1 part 3, a summary of these data
was
prepared
[1]
that
reveals
the main
parameters and their distributions.
5.1
-
tandem, and single axles, the last two of
which are bimodal (similar results are found
in the other European countries).
type
Traffic
As an illustration, table 7 gives, for various
traffics, the distribution of axles between
single, tandem, and tridem axles, while the
following figure gives, for 4 countries, the
distributions
of
the
distances
between
consecutive axles of vehicles.
The peak,
invariably located near 1.2 m, corresponds
to the distances between axles of the same
group, while the modes centered around 3.3
m and 5 m are for single-body and articulated
vehicles, respectively. The next figure shows
the
distributions
of
weights
of
tridem,
(D)
64.7
19.8
15.5
Romano
55.3
26.7
18.0
Auxerre v1
(F)
56.2
16.2
27.6
Auxerre v2
(F)
57.5
16.2
26.3
58.5
20.4
21.1
80.9
12.8
6.3
Brohltal
Highways
Fiano
(I)
(F)
road Angers
Nat.
(F)
Urban way Lyon
M
-
I''-
-
.,
f---,
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t
5
,
•
dLs'tancu between contLguoul axLes
,
t.,
ID
BROS4 IDeulchLandl
Ile--
rr-
Parameters measured
The
flows
(of
trucks
or
axles)
provide
information for the quantification of the
aggressiveness of a traffic in terms of
fatigue of pavements or bridges, but also of
the number of occurences of some loads, useful
for extrapolations. The composition of the
traffic in types of vehicles or of axles is
used to characterize the traffic and its
aggressiveness. It is also important to know
the distances between axles for each type of
vehicle for local effects, in particular for
tandem and tridem axles (groups of axles) ,
which act simultaneously on short distances.
Finally the weights of these axles or groups
of axles are essential to the calculation of
the effects. Their extreme values are used,
after extrapolation, for calibration of the
characteristic values or of models.
- Proportions of axles of each
TABLE 7
.,
r--1
r
8\
A
A
IQ\
2
5
•
$
,
..
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,
dlslances betveen contlguous axles ,.,
POI P02 P14
~ 81fv\ ..
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~
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,
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(Spatn'lI+'121
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Figure 3
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r-
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t-
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Figure 4
161
HEAVY VEHICLES AND ROADS
5.2 - Characteristic axle loads
Various methods of extrapolation have been
proposed within the working group of Eurocode
.1 part 3 in order to determine the weights
of axles having specified return periods; they
yield rather similar results
[12]. These
results are given in table 8 for single,
tandem, and tridem axles. The values having
short return periods are useful for fatigue
loads, while those with long return periods
are used to define the characteristic loads.
Tableau 8 - Extrapolated loads (in kN)
obtained by various methods
Return
period
Item
Extrapolated maximum
loads
Axle
Double
Triple
224 - 226 - 234 252
356 - 353 - 348
332
469 - 436 - 439 442
Axle
2000 years Double
Triple
245 - 278 - 264 295
397 - 442 - 403 379
527 - 487 - 508 517
20 weeks
-
Dynamic coefficient included in the
5.3
measurements
The studies conducted for Eurocode on the
dynamic effects of traffic [13] have made it
possible to quantify the share of dynamic
loads included in the measurements (weighin-motion) and their incidence on the extreme
weight
values.
For
isolated
axles
a
coefficient of 1.15 can be adopted, which
means that 15% of the proposed extreme load
is in reality a dynamic load related to the
vibrations of the vehicles due to pavement
evenness
defects.
The
absolute
dynamic
coefficients to be used in the calculation
of structures must therefore take this into
account. For groups of axles, this coefficient
can be estimated at around 1.10, close to
that found for the total weight of trucks.
So there is approximately 10% dynamic load
assigned to the extremes. For cases involving
static loads (as in traffic jams), it is
therefore necessary to reduce the effects
calculated from the measured traffics proportionally.
6 - MODELS OF LOCAL LOADS - CONCLUSIONS
The calibration of heavy traffic load models
on bridges has been conducted [14] using the
techniques
of
operational
research.
The
effects F of the extrapolated true traffic,
a traffic having a return period of x years,
on some number of characteristic bridges are
defined. The calibration then consists of
minimizing the difference in absolute value
between the effects G of a model and the
values F, assuming that the model can be
broken down into a certain number of para-
162
meters
(number of axles,
load per axle,
distance between axles, etc.), transformed for
the occasion into structural variables of a
linear problem.
6.1 - Extrapolated axle load
The local effects of the true traffic are
determined from extrapolated typical vehicles,
of which the most aggressive are semi-trailers
[12]. They account for about 60% of heavy
traffic.
If we consider a single loaded travel lane,
the maximum axle load measured extrapolated
to the normal quasi-static traffic configuration without congestion does not exceed 220
kN. This value corresponds moreover to extreme
axle loads measured on some routes, on trucks
that are non-uniformly loaded, in violation
(210 kN). The dynamic load is in this case
obtained by mUltiplying this load, in the
worst of cases, by 2.1 for the study of the
general bending of short-span bridges (1.8
for the study of shear) and by 1.3 for the
purely local study [13].
If we now consider two loaded two-way travel
lanes, the maximum axle load is again equal
to 220kN but since the mean speed is lower
in this case, the dynamic load for the
calculation of the general effects is obtained
by multiplying the static load by 1.7, with
no change of the local coefficient.
6.2 - Loading models - Validation
For bridge spans greater than 3 metres, the
optimizations show that the extrapolated true
local traffic, applied to the main travel
lane, can be reduced, from the standpoint of
the equivalent extreme effect, to a TECl-3
tandem. The axle load, dynamic load included,
is 300 kN. The longitudinal distance between
axles is 1.2 metres, the transverse distance
between wheels 2 metres. This tandem therefore
induces on bridges extreme effects close to
those of the true traffic.
Applied to two main traval lanes, contiguous
or not, the true traffic is modelled by 2
tandems acting simultaneously on 2 lanes:
first lane,
the above-mentioned TECl-3
tandem,
- second land, the TECl-3 tandem with twothirds load.
The
contact
surface
of
the
wheels
is
represented by a square measuring 400x400mm2.
The pressure on the ground is not more than
11 bars.
The diffusion through the concrete follows a
slope of 1/1 above the midplane of the
structure.
This load model has been validated on a large
number of bridges. It is on its way to being
adopted as the main model of local characteristic loads under Eurocode 1 (Part 3),
road loads on bridges.
7 - REFERENCES
[1] BRULS A., JACOB B., SEDLACEK G. - Traffic
Data of the European Countries - Eurocode 1
- Part 3 - WG2 (1989)
VEHICLE - BRIDGE INTERACTION
[2] PRAT M. - Local Loads of Traffic on Road
Bridges - Eurocode 1, Part 3, Working Panel
(1989)
[3] SIFFERT M. - Dimensionnement des Chaussees
- Compte-rendu de recherche - LROP (1986)
[4] VIANO A., ELOI - Analyseur de Profil en
Long APL 72 - Notice - LROP (1986)
[5] LUCAS J., DELANNE Y. - Caracteristiques
superficielles des rev~tements routiers - SIA
N· La route, le pneu, le vehicule (1987)
[6] BONAQUIST, CHURILLA, FREUND - Effects of
load,
tire pressure and type on flexible
pavement response (1988)
[7] CANTIENI R.
Dynamic Load Tests on
Highway Bridges in Switzerland - EMPA Report
N" 211 (1983)
[8]
CALGARO
J .A.Action
Dynamique
des
Vehicules Lourds sur un Tablier de Ponts Eurocode 1, Part 3, Working Panel (1988)
[9] OHBD
(1979)
[10] SIA
(1989)
ONTARIO
Standard
HIGHWAY
BRIDGE
Actions
on
DESIGN
Structures
[11] JACOB B., SIFFERT M., An High Performant
WIM System by Piezo-Electric Cables and its
Applications, Int. Symposium on Heavy Vehicles
Weights and Dimensions, Kelowna, BC, Canada
(1986)
[12] JACOB B. & al. - Method for the Prediction of Extreme Vehicular Loads and Load
Effects on Bridges - Eurocode 1 - Part 3 WG8 (1990)
[13] SEDLACEK G. & al. - Definition of Dynamic
Impact Factors - Eurocode 1 - Part 3 - WG5
(1991)
[14] PRAT M.
Calibration
Panel (1992)
Characteristic Local Model
Eurocode 1, Part 3-,. Working
163